mask-pii (Python)

Version: 0.2.0

A lightweight, customizable Python library for masking Personally Identifiable Information (PII) such as email addresses and phone numbers.

It is designed to be safe, fast, and easy to integrate into logging or data processing pipelines.

Official website: https://finitefield.org/en/oss/mask-pii Developed by: Finite Field, K.K.

Features

• Email Masking: Masks the local part while preserving the domain (e.g., a****@example.com).
• Global Phone Masking: Detects international phone formats and masks all digits except the last 4.
• Customizable: Change the masking character (default is *).
• Zero Unnecessary Dependencies: Pure Python implementation.

Installation

From PyPI:

pip install mask-pii

From a local checkout:

pip install -e ./python

Usage

from mask_pii import Masker

masker = (
    Masker()
    .mask_emails()
    .mask_phones()
    .with_mask_char("#")
)

input_text = "Contact: alice@example.com or 090-1234-5678."
output = masker.process(input_text)

print(output)
# => "Contact: a####@example.com or ###-####-5678."

Configuration

The Masker class uses a builder-style API. By default, Masker() performs no masking (pass-through).

Builder Methods

Masking Logic Details

Emails

• Pattern: Detects standard email formats.
• Behavior: Keeps the first character of the local part and the domain. Masks the rest of the local part.
• Example: alice@example.com -> a****@example.com
• Short Emails: If the local part is 1 character, it is fully masked (e.g., a@b.com -> *@b.com).

Phones (Global Support)

• Pattern: Detects sequences of digits that look like phone numbers (supports international +81..., US (555)..., and hyphenated 090-...).
• Behavior: Preserves formatting (hyphens, spaces, parentheses) and the last 4 digits. All other digits are replaced.
• Examples:
  • 090-1234-5678 -> ***-****-5678
  • +1 (800) 123-4567 -> +* (***) ***-4567
  • 12345 -> *2345